1. Field of the Invention
The present field of invention relates to motor vehicle suspension systems.
More specifically, this invention relates to hydraulic damping of all-terrain motor vehicle suspension systems.
In a further and more specific aspect, this invention relates to methods and apparatus for automatically controlling hydraulic dampers in all-terrain motor vehicles suspension systems.
2. The Prior Art
Conventional suspension systems for motor vehicles enhance ride comfort and operating safety by controlling oscillations in a direction substantially normal to the riding surface. These systems substantially comprise a system of springs, dampers, and sensors that are automatically controlled by a computer. These types of suspension systems are commonly referred to as xe2x80x9cactivexe2x80x9d or xe2x80x9csemi-activexe2x80x9d and are employed for use in automobiles manufactured by companies including Toyota, Mercedes-Benz, and Ferrari. Jacques Gordon, Technical Editor for Motor Age describes the state of the art in automobile suspension systems in his February 1999 article, hereby incorporated by reference, xe2x80x9cUnderstanding Electronic Suspension Systemsxe2x80x9d. A great need exists for the transfer of this technology into the all-terrain vehicle market.
Conventional all-terrain motor vehicles are frequently used in recreational sporting activities and can be divided into those having two wheels, commonly known as motorcycles, and those having four wheels, commonly known as quads, sand rails and 4-wheel drive trucks. Track-driven vehicles commonly known as snowmobiles are also frequently used in recreational sporting activities.
All-terrain motor vehicles typically employ suspension systems including springs and hydraulic damping devices, commonly known as shock absorbers. The springs supports the mass of a vehicle operator and the mass of the vehicle chassis, the combination of which is commonly know as a sprung mass. Springs used in conjunction with shock absorbers in conventional suspension systems attempt to isolate the sprung mass of the vehicle from an uneven riding surface, resulting in a smoothened ride. The topography of the typical riding surface can be extreme, ranging from smooth stretches to large jumps. The physical composition of the typical riding surface can also be extreme and includes dirt, rocks, and mud.
Typical shock absorbers include a piston, a damping valve assembly, a connecting rod, a cylinder, hydraulic fluid, and an accumulator. The connecting rod is rigidly attached concentrically to one side of the piston and both translate back and forth inside the cylinder, which is filled with a substantially incompressible hydraulic fluid. The retracting motion, where the free end of the connecting rod and the free end of the cylinder move toward each other, is commonly known as compression. The extension motion, where the free end of the connecting rod and the free end of the cylinder move apart from each other, is commonly known as rebound. As the piston moves relative to the cylinder, hydraulic fluid is forced through the damping valve assembly attached to the piston, imparting a viscous damping force onto the piston and connecting rod. The accumulator compensates for the imbalance in hydraulic fluid volume on either side of the piston created by the presence of a connecting rod. Hydraulic fluid flows into and out of the accumulator during compression and rebound, respectively. Many conventional shock absorbers allow for the independent control of hydraulic fluid flow rate into and out of the accumulator with manually adjustable valves. Since the hydraulic fluid is substantially incompressible, the rate at which it flows into and out of the accumulator directly effects the damping rate.
The prior art proposes various shock absorbers that include a means for automatically controlling damping rates. U.S. Pat. No. 5,850,896 to Tanaka describes an electrically operated shock absorber that includes a pilot chamber and pilot valve which pilot valve is acted on by an electrical solenoid so as to control the damping characteristics of the shock absorber. An arrangement is provided for preventing total bumping of pressure in the pilot chamber in the event of electrical failure and substituting a pressure responsive valve for controlling the damping characteristics when the electrical failure occurs. Unfortunately, existing control systems employed to generate the electrical signals for such a shock absorber do not actively respond to conditions as described by the present invention. For example, U.S. Pat. No. 5,682,968 to Boichot, et al., describes a semi-active suspension system with control circuit having a direct control loop including an inverse model of the damper. The control system described by Boichot does not address variables including engine speed, wheel speed, throttle position, vehicle operator position, and suspension position.
Dynamic response of a hydraulic damper is substantially a function of compression damping rate, rebound damping rate, sprung mass, and spring rate. Damping rates are a function of the rate at which hydraulic fluid flows through the damping valve, and the rate a which hydraulic fluid flows into and out of the accumulator. These flow rates are a function of hydraulic fluid viscosity, hydraulic fluid compressibility, damping valve configuration, and accumulator valve setting. Hydraulic fluid viscosity is a function of hydraulic fluid temperature, which invariably increases during operation in extreme conditions. Unfortunately, an increase in hydraulic fluid temperature typically attenuates damping rates.
The process of optimizing the dynamic response of a hydraulic damper is typically executed manually by the vehicle operator. The optimization process typically requires iteration to obtain acceptable results. The vehicle operator typically adjusts compression and rebound damping rate settings manually with a screwdriver while the vehicle is stopped. Once set, the damping rate cannot easily be changed during operation. Even if the adjustment means were located conveniently, it would be extremely difficult to make manual modifications while operating the vehicle. In the case of optimization immediately prior to an all-terrain motorcycle race, the vehicle operator will typically traverse the racecourse to access and optimize the handling performance of the vehicle over typically extreme conditions of the riding surface. Unfortunately, racing surface conditions can change rapidly and drastically not only during a race, but also during the iterative performance optimization process itself The damping rate settings determined prior to a race may therefore not be the desired settings soon after a race starts, and could result in the creation of adverse conditions for the vehicle operator.
Damping response to high-impact compression on landing from large jumps where the vehicle becomes airborne is usually accessed. All-terrain motorcycles can successfully land on a dirt ramp surface from heights exceeding 25 feet. The desired damping for high-impact compression is high enough to avoid a condition known as bottoming. Bottoming occurs during a high-impact compression when the suspension reaches the limit of its travel and transmits an extreme and undesirable jarring force through the vehicle to the vehicle operator.
Damping response to low-impact compression while traversing the vehicle over acceleration bumps is also usually accessed. Acceleration bumps form inside and at the exit of turns from repeated acceleration of many vehicles through the turns, are spaced approximately 0.5 to 1.0 meters apart peak to peak, and are approximately 10 to 20 centimeters deep. The desired damping for low-impact compression is low enough to avoid a condition known as chassis upset. Chassis upset occurs during low-impact compression when the suspension transmits enough force to the chassis to exceed the ability for the suspension to stay in contact with the riding surface. For example, chassis upset may occur while operating an all-terrain motorcycle. As the vehicle operator attempts to accelerate out of a turn containing acceleration bumps, the suspension may respond in a non-compliant manner and allow the rear tire to temporarily lose contact with the riding surface. If this condition persists, it may cause an undesirable loss in traction, acceleration, and control.
Unfortunately, limitations of conventional suspension damping systems compromise performance when trying to span the full range of extreme riding surface conditions possible. The vehicle operator must make a conscious decision to compromise between compression damping rates. If the compression damping rate is set high enough to avoid bottoming during landing from large jumps, it may induce chassis upset while traversing acceleration bumps. If the compression damping rate is set low enough to avoid chassis upset while traversing acceleration bumps, it may induce bottoming upon landing from large jumps.
The limitations of conventional suspension systems stems from the inability to automatically respond to conditions that could indicate the magnitude of damping required. These variables include engine speed, wheel speed, throttle position, vehicle operator position, vehicle operator mass, suspension position, suspension speed, and hydraulic fluid temperature.
Vehicle operator position has a drastic impact on overall damping performance of all-terrain motorcycles and quads. When in a sitting position on an all-terrain motorcycle or quad, the vehicle operator""s entire body is directly coupled to the vehicle chassis. When standing on the foot pegs of the vehicle, the vehicle operator""s knee joints and legs act as a secondary suspension system. This condition de-couples the vehicle operator""s upper body from the vehicle chassis. The compression and rebound damping requirements are less for the de-coupled condition than for the directly coupled condition. Unfortunately, conventional damping systems cannot automatically compensate for varying vehicle operator position.
Sprung mass also has a drastic impact on overall damping performance of all-terrain motorcycles and quads because vehicle operator mass is substantial relative to vehicle mass. Unfortunately, conventional damping systems cannot automatically compensate for varying vehicle operator mass. This becomes important in the rental market where vehicle operators of different mass operate the vehicle on a daily basis.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent to the prior art. Accordingly, a general object of the present invention is to provide a method and apparatus for advancing all-terrain motor vehicle damping system performance beyond that which any prior art provides. Still further objects and advantages of the present invention will become apparent upon consideration of the drawings and ensuing descriptions.
In order to achieve the objects and advantages of the present invention, first provided is a control system for a hydraulic damper. The control system comprises a means for automatically sensing the magnitude of at least one electrical input signal, a means for automatically processing each input signal through a microprocessor and associated software algorithm to determine an optimum damping rate, and a means for automatically generating an electrical output signal corresponding to the optimum damping rate. The output signal is configured for communication with a hydraulic damper having means for automatically controlling the damping rate according to an electrical signal. Electrical input signals correspond to variables including engine speed, wheel speed, throttle position, vehicle operator position, and suspension position.
Also provided is a method for automatically controlling a hydraulic damper. The method comprises a first step of automatically sensing the magnitude of at least one electrical input signal, a second step of automatically processing each input signal through a microprocessor software algorithm to determine an optimum damping rate, and a third step of automatically generating an electrical output signal corresponding to the optimum damping rate. The output signal is configured for communication with a hydraulic damper having means for automatically controlling the damping rate according to an electrical signal. Electrical input signals correspond to variables including engine speed, wheel speed, throttle position, vehicle operator position, and suspension position.